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The Earth is dramatically carbon poor comparing to the interstellar medium and the proto-sun. The carbon to silicon ratios in inner solar system objects show a correlation with heliocentric distance, which suggests that the destruction of carbon grains has occurred before planet formation. To examine this hypothesis, we perform model calculations using a chemical reaction network under the physical conditions typical of protoplanetary disks. Our results show that, when carbonaceous grains are destroyed and converted into the gas phase and the gas becomes carbon-rich, the abundances of carbon-bearing species such as HCN and carbon-chain molecules, increase dramatically near the midplane, while oxygen-bearing species such as H2O and CO2 are depleted. The carbon to silicon ratios obtained by our model calculations qualitatively reproduce the observed gradient with disk radius, but there are some quantitative discrepancies from the observed values of the solar system objects. We adopted the model of a disk around a Herbig Ae star and performed line radiative transfer calculations to examine the effect of carbon grain destruction through observations with ALMA. The results indicate that HCN, H13 CN and c-C3 H2 may be good tracers of this process.
Boulders are ubiquitous on the surfaces of asteroids and their spatial and size distributions provide information for the geological evolution and collisional history of parent bodies. We identify more than 200 boulders on near-Earth asteroid 4179 Toutatis based on images obtained by Chang'e-2 flyby. The cumulative boulder size frequency distribution (SFD) gives a power-index of −4.4 ± 0.1, which is clearly steeper than those of boulders on Itokawa and Eros, indicating much high degree of fragmentation. Correlation analyses with craters suggest that most boulders cannot solely be produced as products of cratering, but are probably survived fragments from the parent body of Toutatis, accreted after its breakup. Similar to Itokawa, Toutatis probably has a rubble-pile structure, but owns a different preservation state of boulders.
A comparison of the Jovian and Saturnian rings is made by reviewing the recent advances in planetary spacecraft exploration and theoretical study. Two main issues are addressed, namely, the different structures of these two planetary ring systems and the water ice composition of the Saturnian rings. It is suggested that answers might be found by invoking tidal capture of Trans-Neptunian Objects with highly differentiated structures even though catastrophic breakup of pre-existing satellites in the ring regions remains a real possibility. Erosion mechanisms such as meteoroid impact, photo-sputtering, orbital instability of charged dust particles and thermal evaporation acting at different time scales could lead to the preservation of the Saturnian ring system but not the Jovian ring system of large mass originally.
Mercury is in all sense of the words still Terra Incognito, its magnetosphere is hence little known. The only source of knowledge came from the in-situ measurements by the Mariner 10 close encounters in 1974. This has been complemented since by ground-based observations of the atomic sodium and potassium emissions in the vicinity of the planetary disk. This series of optical observations has produced intriguing evidence of magnetospheric and/or solar wind effects on the surface-plasma interaction processes. In this review we will describe the current theories of the corresponding space weather effects.
The existence of a population of large planetoids outside the orbit of Neptune predicted by GP Kuiper, KE Edgeworth and JA Fernandez has been confirmed by ground-based observations.The physical properties of these Kuiper Belt Objects (KBOs) remain elusive. Photometric measurements have indicated that they have diverse color variations. A theoretical model is formulated to simulate the evolution of the surface materials of the KBOs under the influence of cosmic ray irradiation and meteoroid impacts. The long-term goal is to couple this theoretical model to observations and laboratory experiments such as LARA (Laboratory Astrochemistry and Astrophysics).
The collisions of comet Shoemaker-Levy 9 with Jupiter have produced many surprising auroral and magnetospheric phenomena. The energy released during the passage of the cometary dust comas through the jovian magnetosphere and at atmospheric explosion could lead to impulsive particle acceleration, enhanced radial diffusive transport, and the establishment of field-aligned current systems connecting the comet impact sites to their respective magnetic conjugate points. Some of the observed effects such as the abrupt increase of decimetric radio emission, the excitation of infrared emissions and mid-latitude auroral emission in the ultraviolet, could be interpreted within the framework of these mechanisms. Several auroral features like the X-ray outbursts and short-term variations in the UV emissions are more puzzling and require further observation of jovian auroral dynamics in these wavelength ranges in coordination with the Galileo mission.
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